A variety of temperature sensors can be used in environments that require the temperature sensor to be contained within a protective sheath. For example, the temperature sensors can be used in applications, such as high temperature and/or high pressure processes, that require that the sensor be protected to some degree from the extreme environment. In some applications, the protective sheath is made of a conductive material that is electrically grounded in the setup in which the temperature sensor is deployed. In many setups, the temperature sensor is configured as a thermocouple with a junction point that also is electrically grounded, thereby providing the ability to make a direct measurement of temperature. For example, the thermocouple can be electrically grounded by electrically coupling the thermocouple to the conductive sheath. The sheath is filled with an electrically insulative material to isolate the conductors making up the thermocouple from each other and from the inner wall of the sheath (except for the junction point). However, because the junction point is grounded to the sheath, a measure of the insulation resistance of the temperature sensor (i.e., a measure of the integrity of the electrically insulative material isolating the conductors from each other and from the inner wall of the sheath) cannot be made. Accordingly, an imminent failure of the temperature sensor may go undetected until the sensor actually fails. Inaccuracies in temperature measurements also may go undetected. As an example, a welding operation performed in the vicinity where the temperature sensor is installed can interfere electrically with the measurement made by a grounded sensor.